1. Field of the Invention
The present application relates to a method and machine for forming splines on a power transmission member, such as a clutch hub for a vehicle automatic transmission, and to the splined member that is formed thereby.
2. Description of the Prior Art
Power transmission members to which this invention relates are utilized to couple rotary drive and driven members. These types of members may be utilized in many different environments, such as speed reducing gear units, other transmissions with multi-speed outputs such as vehicle transmissions, etc. These power transmission members may take many forms. One type includes splines that receive complementary splines on another member to provide a rotary driving relationship therebetween. This type of splined member may be embodied as a solid splined shaft or a member having an annular sleeve portion of a thin-walled construction where the splines are formed. This latter type of splined member is the type to which the present invention is directed.
Vehicle automatic transmissions incorporate the type of power transmission member to which this invention relates. These transmissions include a number of drive trains through which rotary power is transmitted from the vehicle engine to its driving wheels. The drive trains of the transmission each include one or more clutches in engaged or disengaged conditions to couple or disconnect the engine from the driving wheels through that particular drive train. Within each clutch, two rotary clutch components are either coupled for rotary movement with each other or uncoupled so that one rotates without the other in order to establish the engaged or disengaged condition of the clutch.
The coupling and uncoupling of clutch components within a vehicle automatic transmission clutch is accomplished by the use of clutch discs and a power transmission member embodied as a clutch hub. The clutch hub is mounted on one of the rotary clutch components and has a thin-walled annular sleeve portion that receives a number of annular clutch discs in a stacked relationship. The clutch discs may either be mounted about the exterior of the sleeve portion or within the interior thereof and have either their outer or inner peripheral edges formed with splines that are received by complementary splined configurations on the sleeve portions so as to be rotatably fixed with respect to the clutch hub and the clutch component on which the hub is mounted. The other clutch component also has a number of thin clutch discs rotatably fixed to it and received in an alternating manner between the clutch discs associated with the clutch component carrying the hub. The clutch discs are axially slidable with respect to the clutch hub so that a fluid motor of the clutch can frictionally engage the stacked clutch disc arrangement upon being supplied with a fluid pressure to thereby interconnect the two clutch components for rotation with each other. Upon termination of the supply of fluid pressure to the motor of the clutch, the clutch discs can frictionally slide at their engaged surfaces to allow relative rotation between the two clutch components. The sleeve portion of the hub usually has lubrication ports through which a lubricant for the clutch flows.
The type of automatic transmission clutch hub described above generally has a somewhat cup-shaped configuration with an annular end wall used to mount the hub as well as the annular sleeve portion having the thin-walled construction where the clutch hub splines are formed. The end wall extends radially in an inward direction from one end of the sleeve portion which extends axially. Conventionally, the splines have been formed by first placing an unsplined hub blank on a mandrel and then performing an impact operation using suitable dies. Usually, this impact operation has been performed using two dies oriented in a 180.degree. opposed relationship so that the splines are formed by forceful movement of each die toward the other with the mandrel and the clutch hub blank between the dies. The dies thus impact the clutch hub in an aligned relationship with respect to each other to balance the impact forces on the mandrel. A number of strokes are performed to form each spline, proceeding from the end wall toward the open end of the hub. After each spline is formed, the mandrel is rotated slightly to permit the splines to be formed adjacent the previously formed ones. A one-half revolution of the mandrel and clutch hub blank thus completes the splining to form a splined clutch hub for a vehicle automatic transmission.
The spline forming described above causes a work hardening of the metallic material, i.e. steel, from which the hubs are made. This work hardening makes the sleeve portion less tough and more brittle. Also, the sleeve portion is deformed axially along the splines. The axial deformation distorts the flatness of the radial end wall of the hub used to mount it. Lubrication ports formed in the sleeve portion of the hub cannot be made prior to the spline forming because the axial deformation of the sleeve portion would distort the configuration of the ports.
Prior art patents which are somewhat similar to the teachings of the present invention are described below; but important differences therebetween will be readily apparent to those skilled in the art.
U.S. Pat. No. 3,214,951 discloses apparatus for rolling teeth on tubular elements which utilizes elongated dies that cooperate with a smooth cylindrical mandrel received within a tubular element to be splined. Longitudinal sliding movement of the dies in a parallel fashion with respect to each other on opposite sides of the mandrel forms teeth on the tubular element by forcing cold flow of the material of the tubular element. The interior surface of the tubular element remains undeformed and smooth due to the support provided by the smooth outer surface of the mandrel on which the tubular element is mounted.
U.S. Pat. No. 3,407,638 discloses a method for forming serrated or corrugated hollow tubes wherein a toothed mandrel is positioned within a hollow tube and then positioned between two rotating dies. Engagement of the rotating dies with the hollow tube mounted on the mandrel then causes tube deformation to serrate or corrugate the tube. The rotational position of the rotating dies must be maintained accurately along a single diameter of the axis of mandrel rotation or, otherwise, the force load applied to the mandrel will be unbalanced. A similar corrugating operation is performed by a machine disclosed by U.S. Pat. No. 3,630,058.